1. Field of the Invention
The present invention relates generally to an asynchronous CDMA mobile communication system, and in particular, to an apparatus and method for coding/decoding TFCI (Transport Format Combination Indicator) bits for transmission of DSCH (Downlink Shared Channel) data in a hard split mode.
2. Description of the Related Art
A downlink shared channel (DSCH) is commonly used by a plurality of users on a time-division basis. The DSCH is associated with a dedicated channel (DCH) for every user. The DCH includes a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH). In particular, the DPCCH is used in association with the DSCH. Therefore, the DPCCH is used as a physical control channel for the associated DCH and the DSCH. The DPCCH includes information on a TFCI (Transport Format Combination Indicator), one of many control signals. The TFCI is information indicating a transport format of data transmitted over the physical channel. Therefore, the TFCI information includes information on both the DCH and the DSCH.
The TFCI information is comprised of 10 bits, and the 10-bit TFCI information is encoded into 30-bit. The encoded 30 bits are transmitted on the DPCCH.
Simultaneously transmitting TFCI for the DCH and TFCI for the DSCH over the DPCCH is divided into two methods: a hard split method and a local split method.
The TFCI for the DCH is referred to as a TFCI field#1 or a first TFCI, and the TFCI for the DSCH is referred to as a TFCI field#2 or a second TFCI.
In the hard split method, the TFCI field#1 and the TFCI field#2 are indicated with 5 bits, respectively, and then, encoded with a (15, 5) punctured bi-orthogonal code. Thereafter, the 15-bit TFCI field#1 and TFCI field#2 are multiplexed into 30-bit TFCI field#1 and TFCI field#2, and then, transmitted over the physical channel.
In the logical split method, the TFCI field#1 and the TFCI field#2 are encoded into one TFCI with a (30,10) punctured Reed-Muller code (or sub-code second order Reed-Muller code). In this method, the information bits of the TFCI field#1 and the TFCI field#2 are divided in a specific ratio. That is, the 10 information bits of the TFCI field#1 and the TFCI field#2 are divided in a ratio of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or 9:1. The TFCI field#1 and the TFCI field#2, after being divided in a specific ratio, are encoded with a block code, i.e., the (30,10) punctured Reed-Muller code.
FIG. 1 illustrates a structure of a transmitter utilizing the hard split method. Referring to FIG. 1, a (15,5) bi-orthogonal encoder 100 encodes a 5-bit TFCI field#1 for the DCH into 15 coded symbols, and provides the 15 coded symbols to a multiplexer 110. At the same time, a (15,5) bi-orthogonal encoder 105 encodes a 5-bit TFCI field#2 for the DSCH into 15 coded symbols, and provides the 15 coded symbols to the multiplexer 110. The multiplexer 110 then time-multiplexes the 15 coded symbols from the encoder 100 and the 15 coded symbols from the encoder 105, and outputs 30 symbols after arrangement. A multiplexer 120 time-multiplexes the 30 symbols output from the multiplexer 110 and other signals, and provides its output to a spreader 130. The spreader 130 spreads the output signal of the multiplexer 120 with a spreading code provided from a spreading code generator 135. A scrambler 140 scrambles the spread signal with a scrambling code provided from a scrambling code generator 145.
FIG. 2 illustrates a procedure for exchanging signaling messages and data between a Node B and RNCs (Radio Network Controllers) for the hard split method defined in the existing 3GPP (3rd Generation Partnership Project). Referring to FIG. 2, if transmission data of the DSCH is generated, a radio link controller (RLC) 11 of an SRNC (Serving RNC) 10 transmits the DSCH data to a MAC-D (Medium Access Control-Dedicated channel) 13 of the SRNC 10 in step 101. A primitive transmitted at this moment is MAC-D-Data-REQ. In step 102, the MAC-D 13 of the SRNC 10 transmits DSCH data received from the RLC 11 to a MAC-C/SH (MAC-Common/Shared channel) 21 of a CRNC 20. A primitive transmitted at this moment is MAC-C/SH-Data-REQ. In step 103, the MAC-C 21 of the CRNC (Control RNC) 20 determines (schedules) a transmission time for the DSCH data received in the step 102 from the MAC-D 13 of the SRNC 10, and then, transmits the DSCH data and its associated TFI (Transport Format Indicator) to an L1 (Layer 1) 30 of a Node B (hereinafter, the term “Node B” refers to a base station). A primitive transmitted at this moment is MPHY-Data-REQ. In step 104, the MAC-D 13 of the SRNC 10 transmits transmission data of the DCH and its associated TFI to the L1 30 of the Node B. A primitive transmitted at this moment is MPHY-Data-REQ. The data transmitted in the step 103 is independent of the data transmitted in the step 104, and the L1 30 of the Node B generates a TFCI, which is divided into a TFCI for the DCH, and a TFCI for the DSCH. In the steps 103 and 104, the data and the TFIs are transmitted using a data frame protocol.
After receiving the data and the TFIs in the steps 103 and 104, the L1 30 of the Node B transmits the DSCH data over a physical DSCH (PDSCH) to an L1 41 of a UE (User Equipment; hereinafter, the term “UE” refers to a mobile station) 40 in step 105. Thereafter, in step 106, the L1 30 of the Node B transmits the TFCI to the L1 41 of the UE 40 using the DPCH. The L1 30 of the Node B transmits the TFCIs created with the TFIs received in the steps 103 and 104, using the fields for the DCH and the DSCH.
FIG. 3 illustrates a procedure for exchanging signaling messages and data between Node Bs utilizing the logical split method. Referring to FIG. 3, if DSCH data to be transmitted is generated, an RLC 301 of an RNC 300 transmits the DSCH data to a MAC-D 303 of an RNC 300 in step 201. A primitive transmitted at this moment is MAC-D-Data-REQ. Upon receipt of the DSCH data from the RLC 301, the MAC-D 303 transmits the DSCH data to a MAC-C/SH (MAC-Common/Shared channel) 305 in step 202. A primitive transmitted at this moment is MAC-C/SH-Data-REQ. Upon receipt of the DSCH data, the MAC-C/SH 305 determines a transmission time of the DSCH data and then transmits a TFCI associated with the DSCH data to MAC-D 303 using primitive transmission in step 203. After transmitting the TFCI to the MAC-D 303 in the step 203, the MAC-C/SH 305 transmits the DSCH data to an L1 307 of the Node B in step 204. The DSCH data is transmitted at the time determined (scheduled) in the step 203. Upon receipt of the TFCI for the DSCH data transmitted from the MAC-C/SH 305 in the step 203, the MAC-D 303 transmits the TFCI information to the L1 307 of the Node B in step 205. The MAC-D 303 also transmits the DCH data and the TFI for the DCH data. A primitive transmitted at this moment is MPHY-Data-REQ.
After transmitting the TFCI for the DSCH, the MAC-D 303 determines a TFI for the DCH, and transmits the DCH data along with the TFI to the L1 307 of the Node B in step 206. A primitive transmitted at this moment is DCH-MPHY-Data-REQ. The DSCH data transmitted in the step 204 and the TFCI information transmitted in the step 205 are related to the time determined in the step 203. That is, the TFCI information in the step 205 is transmitted to a UE 310 over the DPCCH at a frame immediately before the transmission of the DSCH data in the step 204 over the PDSCH. In the steps 204, 205 and 206, the data, the TFCI and the TFIs are transmitted using a frame protocol. Particularly, in the step 206, the TFCI is transmitted through a control frame. In step 207, the L1 307 of the Node B transmits the DSCH data over the PDSCH to an L1 311 of the UE 310. In step 208, the L1 307 of the Node B creates a TFCI using the TFIs received in the step 206, and transmits the created TFCI over the DPCH to the L1 311 of the UE 310. More specifically, the L1 307 of the Node B creates the TFCI using the TFIs received in the step 206, and transmits the created TFCI on the DPCCH.
Summarizing the logical split method, the MAC-C/SH 305 transmits DSCH scheduling information and TFCI information of the DSCH to the MAC-D 303 in the step 203. This is because in order to encode the TFCI for the DSCH and the TFCI for the DCH in the same coding method, the MAC-D 303 must simultaneously transmit the DSCH scheduling information and the TFCI information to the L1 307 of the Node B. Therefore, when the MAC-D 303 has data to transmit, a delay occurs until the MAC-D 303 receives the scheduling information and the TFCI information from the MAC-C/SH 305 after transmitting the data to the MAC-C/SH 305. In addition, when the MAC-C/SH 305 is separated from the MAC-D 303 on the lur (an interface between the SRNC and the DRNC), i.e., when the MAC-C/SH 305 exists in the DRNC (Drift RNC) and the MAC-D 303 exists in the SRNC, the scheduling information and the TFCI information are exchanged on the lur, causing an increase in the delay.
Compared with the logical split method, the hard split method can reduce the delay because information transmission to the MAC-D is not required after scheduling in the MAC-C/SH. This is possible because the Node B can independently encode the TFCI for the DCH and the TFCI for the DSCH in the hard split method. In addition, when the MAC-C/SH is separated from the MAC-D on the lur, i.e., when the MAC-C/SH exists in the DRNC and the MAC-D exists in the SRNC, the scheduling information is not exchanged on the lur, preventing an increase in the delay. However, according to the foregoing description, the information amounts (bits) of the TFCIs for the DCH and the DSCH are fixedly divided in a ratio of 5 bits to 5 bits, so that it is possible to express a maximum of 32 information for the DCH and 32 information for the DSCH. Therefore, when there are more than 32 information bits for the DSCH or DCH, the hard split mode cannot be used.